I'm pretty new at this but have learned more than I should be reading too much!

I understand that your boil volume effects the hop utilization; more boil volume = more IBU's from the same hop quantity.

My question is about "Average Boil Volume".

Lets say my recipe calls for an average boil volume of 3.5 gallons (Partial boil) in order to give me 37 IBU's. Does this mean I should start the boil with 3.5 gallons or does this mean that over the entire 60 min boil I should average 3.5 gallons? If it means the latter then I would need to start with around 4.0 gallons so that I have around 3.0 gallons left at flame out due to evaporation loss so that I average 3.5 gal.

??

Just need clarification. I don't want my IBU's to be messed up because I don't understand what the calculators are asking for with "Average Boil Volume".

would need to start with around 4.0 gallons so that I have around 3.0 gallons left at flame out due to evaporation loss so that I average 3.5 gal.

yes, but I would work it out so i end up with a 3.5 final volume The less top up the better.
You can either lower the heat so your boil off rate decreases (preffered)
or up your primary volume (if your kettle can handle it)

Whaaaat....since when does boil volume = more IBU from same hop quantity. That is complete malarchy. While there are some that agree that there is better hop utilization in higher wort volume....this in no shape or form would mean that your final IBU value would be better. Think about this logically, sure you get better hop utilization per oz, but your final volume is also going to be larger, meaning the IBU's (dependent on volume) will be drastically different. If increased boil volume = more IBU's, then why don't commercial breweries just use an oz of hops for 15 bbl.....because YOU CAN'T!!!

Whaaaat....since when does boil volume = more IBU from same hop quantity. That is complete malarchy. While there are some that agree that there is better hop utilization in higher wort volume....this in no shape or form would mean that your final IBU value would be better. Think about this logically, sure you get better hop utilization per oz, but your final volume is also going to be larger, meaning the IBU's (dependent on volume) will be drastically different. If increased boil volume = more IBU's, then why don't commercial breweries just use an oz of hops for 15 bbl.....because YOU CAN'T!!!

That's what is confusing to me because most everyone supports the whole higher boil volume = higher IBU including the beer recipe calculators. I never did fully believe that if you end up with the same volume going into the fermenter with top off that you can drastically change the IBU's in that volume just by boiling less or more water during the hop additions.

ok...you're partially right. but you are confusing isomerization/utilization with IBU's. Yes, both deal with hops, but IBU's are entirely dependent on the volume of the wort and although this has been debated, the gravity of the wort (hence why some people do a "hop tea". However, the point that you are missing is that although isomerization supposedly is "better" at a higher volume/lower gravity....there is a limit of saturation where you will be defeating the purpose of adding volume just for the sake of more IBU's. you will still have to boil down to the intended post boil volume, or at least very close to it to get to the IBU's that you actually want. Think about it logically. 1 oz of hopd in a 5 gallon batch and 1 oz in a 10 gallon batch. The 10 gallon batch will not have 50% less IBU's than the 5 gallon batch because the isomerization potentially was better, but the fact remains that the IBU's ARE LESS!!!! It's not linear....but they are less!!!!!